This invention relates to an article having a non-planar surface with a high-resolution pattern formed thereon and a method of making the article comprising use of an elastomeric relief member. The invention is particularly useful in fabricating distributed-feedback ridge waveguide lasers and other structures in integrated optics that rely on gratings or photonic crystals formed on non-planar surfaces.
In the fields of optics and electronics, there is continuing interest in developing smaller-sized devices, e.g., devices that consume less space, use less power, operate more quickly, and exhibit higher performance than their larger counterparts. Low cost devices affordable to consumers are sought. The drive toward miniaturization has precipitated the development of new materials for use in optic and electronic devices and new techniques of fabrication.
Recently, interest has grown in electronic devices that use organic materials as conducting, semiconducting, and light-emitting materials. Organic materials are attractive for use in optic and electronic devices as they are compatible with plastics and can be easily fabricated to provide low-cost, lightweight, and flexible devices with plastic substrates. For example, low cost, electrically-pumped lasers could be made supported by lightweight, flexible plastic substrates. Simple fabrication techniques combine with the relative ease of processing and depositing organics to allow rapid prototyping of new resonator designs and the cost-effective commercialization of plastic laser technologies.
New patterning methods also are being explored to provide higher resolution patterns in conventional materials (SiO2) so that devices with small features can be made easily in geometries and fabrication sequences that are incompatible with traditional patterning techniques. Many non-conventional patterning methods having sub-micron resolution are currently being explored including microcontact printing, molding and embossing. See D. Qin, xe2x80x9cMicrofabrication, Microstructures, and Microsystems,xe2x80x9d TOPICS IN CURRENT CHEM. (1998), at p. 1-20, discussing various patterning techniques, which is hereby incorporated herein by reference. Molding techniques have not, however, been exploited to directly pattern gain materials for laser applications. In addition, although printing methods have been used to form planar resonators, they have not been used to form resonators directly on non-planar structured surfaces that are difficult to pattern using conventional methods.
There is an increasing need to develop simple methods for forming high-resolution patterns on non-planar surfaces, for example, for distributed feedback (DFB) laser devices that have applications in integrated optics, in optical measurement, communication and transmission, optical recording, laser printers, and the like. A ridge waveguide type DFB semiconductor laser includes a semiconductor substrate having protruding stripe-like ridge layers with diffraction gratings formed on the surface of the ridge layers. Methods for successfully applying micro-printing and molding techniques have not been applied to provide high-resolution patterns in fabricating diffraction gratings and resonator structures for applications in integrated optics. Also, none of the conventional lithographic methods (holographic exposure, photolithography, electron-beam lithography, etc.), can be used to form high-resolution patterns directly on non-planar surfaces, such as those of ridge waveguides, because it is impossible to form uniform layers of resist on non-planar surfaces using standard procedures such as spin-casting and spraying. Thus, DFB ridge-type lasers have been fabricated by first forming a pattern or grating on a planar surface, followed by forming the ridge. See, e.g., U.S. Pat. No. 5,880,028 issued Mar. 9, 1999 to Yamamoto et al, xe2x80x9cRidge Waveguide Type Distributed Feedback Semiconductor Laser Device and Method for Manufacturing the Same,xe2x80x9d which is hereby incorporated by reference. This approach demands a specific sequence for the patterning (e.g., the high-resolution features must be defined before the ridges), which among other things inhibits flexibility.
As may be appreciated, those concerned with technologies involving optic and electronic devices or systems continue to search for new methods of patterning substrates, including non-planar substrates, that enable more flexible processing and reduced cost. In particular, it would be advantageous to provide a high-resolution patterning technique that may be used in directly patterning non-planar surfaces, e.g., for use in fabricating ridge waveguide structures.
Summarily described, the invention comprises an article including an electronic or optical device, in which the device has a substrate with a non-planar surface. A high-resolution patterned layer is formed directly on the non-planar surface with use of a relief member, preferably a flexible member, that can impose, by contact, a pattern on the non-planar surface. The device may be comprised of a plurality of materials including plastic or glass or at least one material selected from the group of poly(p-phenylene vinylene) (PPV), silica glasses, cellulose acetate, KH2PO4 (KDP), polysterene microspheres, polyimide, polyester, and polymethylmethacrylate. In a preferred embodiment, the device comprises a distributed-feedback ridge waveguide structure. A method for forming the device comprises providing an elastomeric member having relief geometries on its surface defining a pattern; contacting the non-planar surface of the substrate with the elastomeric member so that the pattern of the elastomeric member is imposed on the non-planar surface; and shaping portions of the non-planar surface following the pattern imposed by the elastomeric member to define the patterned layer. This method may comprise a printing or molding procedure.